Louisiana, coastal advocates push the Corps to keep a new cut in the Mississippi River open
Louisiana’s coastal authority and advocates continue to fight the U.S. Army Corps of Engineers over the future of a new cut along the Mississippi River on Plaquemines Parish’s east bank. But as it stands, the odds aren't in their favor as the final decision on whether the channel will remain open looms, with the potential to come down in the next few months.
Chugging through lush, emerging marsh in Bay Denesse near the new channel, Restore the Mississippi River Delta Coalition advocates argued nature has gifted them with another prime location to study how the river builds land in a time when the future of Louisiana’s lower third depends on slowing the rapid erosion of its coastline.
“We've been asking and working toward the large-scale diversions for 35 years, and this just happened,” said Kim Reyher, the Coalition to Restore Coastal Louisiana’s executive director. “And so we wanna do everything we can to maximize the value of this and not shut it down abruptly.”
The crevasse, now known as Neptune Pass, widened substantially since the 2019 flood when experts suspect a rock dam shrinking the channel’s once narrow entrance failed, unable to withstand a strong punch from the Mighty Mississippi. In three years, it’s grown sixfold and scoured out a nearly 90-foot-deep crater near its opening.
It wasn’t until this spring that it caught the attention of the federal and state government after the Corps said the water’s redirection slowed the river enough to affect navigation in the main shipping channel. But sand wasn’t only building up in the Mississippi River. Satellite imagery showed shoaling and the start of delta formation where the new crevasse meets Quarantine Bay. An area that was once 8 feet deep has started filling in, now just 2 feet deep and solid enough to walk on.
While the Corps’ primary mission is to protect navigation, Neptune Pass’ land-building potential muddies the water. Louisiana’s Coastal Protection and Restoration Authority officials said more study is needed to strike the right balance between preserving the shipping channel and restoring some of the land that the state has lost, largely due to disconnecting the river from the surrounding marshes.
“We need to get past knee-jerk reactions to a changing river,” Theryn Henkel, a coastal resources scientist for CPRA, said on Monday’s tour of the east bank.
The issue has come to a head as the state waits to see if the Corps will approve its $2 billion proposal to build a channel to divert Mississippi River water a few miles upstream through the Plaquemines Parish’s west bank into the degraded marshes of Barataria Bay to rebuild and nourish the area. The final decision is expected by the end of the year.
Currently, the Corps is completing an environmental assessment while designing a closure structure for Neptune Pass’ opening. Their first choice would stop the vast majority of water from entering the channel, leaving just enough room for small boats to navigate through. Without some sort of control in place, the channel has the potential to grow even more.
CPRA and the National Wildlife Federation are working to commission their own study in order to have on hand numbers that show how much sediment is coming through Neptune Pass and what kind. That will help them, as well as the Corps, figure out how the new connection is building land. Is it a redistribution of mud through erosion or are enough sands, silts and clays coming through to stack up?
Taking the time to find answers to their questions before shutting the channel down would be a start, said Amanda Moore, NWF’s Gulf Program Director.
“This is a great place to set the tone,” she said. “It’s an opportunity for us to manage for both navigation and restoration.”
While neither CPRA nor the coastal restoration groups have specified alternatives to the Corps’ closure plans, Henkel said the bottom line is to maintain as much water flow through the channel as possible, while balancing shipping needs. That could mean creating a partial closure that narrowed Neptune Pass’ entrance while leaving it relatively deep, as studies have shown the “best sediment” sits at lower depths in the Mississippi River, Henkel said.
The Army Corps has already dropped about 90,000 tons of stone to cover the crater at the head of Neptune Pass with a rock blanket to prevent further erosion in August, said spokesman Ricky Boyett.
They expect to release their environmental assessment by the end of the month and open a 30-day public comment period once it's published. The final design decision will come after the Corps addresses the comments received.